String-of-exchanges telephone system



Jan. 17, 1950 B. A. WALLACE 2,495,191

STRINGOF-EXCHANGES TELEPHONE SYSTEM Filed Aug. 2, 1946 4 Shee'ts-Sheet 1INVENTOR BERT A.WALLACE BY gi ATTORNEY B. A. WALLACE STRINGOFEXCHANGESTELEPHONE SYSTEM Filed Aug. 2, 1946 4 Sheets-Sheet 4 Fla. 5

RIOO' INVENTOR: BERT A. WALLACE BYW ATTORNEY Patented Jan. 17, 1950UNITED STATES PATENT OFFICE STRING- GF-LEXCHANGES TELEPHONE SY STE BertA. Wallace, "Chicago, 111., assignor to Kellogg Switchboard and SupplyCompany, Chicago, 111., a-corporation of Illinois Application. August 2,1946, SerialNo. 1688,1037

(Cl. j17 9-*2.7)

13 Claims.

1 'This invention relates to string-of-exchanges telephone systems. Itsgeneral object is'toprovide new and improved signalling arrangements foruse in a system wherein three or more telephone exchanges are served bya group of common trunk lines.

GENERAL DESCRIPTION the concerned area, and wherein interchangeconnections involving .any one of therural ex? changes are handled on atool basis byanoperator in the main exchange.

Features of the disclosed system include the provision that seizureofanidleoneof the common trunk lines at any exchange guards it againstfurther seizure at all exchanges, and the further provision that thesignalling apparatus in the main exchange is so controlled from therural exchanges as to give the operator the callingsignal andsupervisory-signal indications customarily employed in c'ommon batterymanual practice.

ther objects and features of the invention will become more apparent as"the description progresses.

Figs. 1 to "3 of the accompanying'drawings-show apparatus locatedrespectively in the main ex-- change M, in .a rural automatic .exchange1R1 occupying an intermediate position along the 'group of common trunklines,;and:in;rural auto- -matic exchange RT whereat the :commontrunk:lines terminate; Fig. 4:. ShOWSia modificdrarrange ment for use in themain exchange and in the intermediate exchanges; and .Fig. .5 ":is aschematic diagram showing the group {of common trunk lines TLextendingirom mainrexchange -M to the terminating rural exchange -RT, byway of intermediate rural exchanges :including RI and R2.

As previously indicated, calls localto. any rural exchange are handledin the usual manner through the automatic switching. apparatus therein,while all interexchange calls including .any one of the rural exchanges,whether from one rural exchange to another, or'to or from a .line of themain exchange, or'beyond, are handled over one or another of the commontrunkllines TL by an operator in .the main exchange.

An interexchange arrangement ofv the type un- "2 der discussion ,is of.particular utility in a telephone system serving small communities,villages, and thelike, located a view miles apart and comparatively neara larger community or city whereat the main exchange is located. Amultiexchangesystem of this general type is discussed on page .190 ofAutomatic Telephonesystems', by William Aitken; Van Nostrand Co., 1923.

In the system herein illustrated,'each rural exchange mayhave-anominalcapaeity of lines, and employs finder-connector links forinterconnecting local lines with each other and with the common trunklines.

It has been chosen to illustrate the invention as applied to a system ofthe foregoing character wherein thercommon trunk lines are providedrespectively with superimposed differential-duplex telegraph-circuits,for carrying the signals necessary for the intended operation. Only oneof the trunk .lines T-Lbf Fig. 4 is shown in the circuit drawings (Figs.1 to 3) .but it has been chosen to illustrate circuit apparatusassociated with this trunk line suitable for use when two .pairs ofconductors are employed in the wellknown phantom arrangement to providethree trunk lines (the .tWoso-called side circuits andtheso-calledphantomcircuit). In such an arrangement,.socalled compositetelegraph circuits are superimposed on three of the four physicaltalking conductors to provide individual duplex telegraph lines for thethree trunk lines.

The toll line ,TL illustrated in Figs. 1 to 3 is .carriedover one oftheside. circuits of the three.- circuit combination, while conductorsI2 3 at repeating coil H8, 224 ,at repeating coil 2H8, and

v.324 at repeatingcoil i318, represent the neutral connections to suchside circuit in the three illustrated exchangesfor one side of thephantom trunk line.

In .the ,mainexchange ,(Fig. 1), the terminating equipmentior the tollline TL includes a pair of condensers l2! .for separating the conductors.[23 from each. other incidentto derivation of the two compositetelegraph circuits thereover, iso- .l'ating repeating coil 1 i8,retardcoils H9, antithump condensers I'2ll,,the terminatingdilierential-duplex telegraphrepeateriRHill, and jack J2.

The illustrated.main-exchange equipment further includes calling deviceCD which can be connected with the terminating repeater RID!) of any ofthe common trunk lines (as by way of thekey K individual to theillustrated trunk line 'TL) and includes the imanual common-battery'l'ine circuit LC and jack J! for the'line of manual substation I00, andthe operators common-battery cord circuit CC, having its plugs PI andP2.

The equipment shown in Fig. 2 for the rural intermediate exchange RIincludes parts 2I9 to HI (and 2 I9 to 22I) corresponding respectively toparts II9 to I2I of Fig. 1; the intermediate difierential-duplextelegraph repeater R200; 10- cal repeater R225 and associated exchangeselector S200; finder F200 and connector 0200 which may complete aconnection to the line of local station I 33I; finder F250 and connectorC350 which may complete a connection from local station I34I to thetrunk line TL by way of branch 249; and repeater R250 associated withbranch 249.

The items of circuit apparatus shown in Fig. 3 for the rural terminatingexchange RT are generally duplicates of corresponding apparatusillustrated in Fig. 2, except that the terminating differential-duplextelegraph repeater R300 is much simpler than repeater R200 of Fig. 2,and more nearly resembles repeater RI00 (Fig. 1) in the main exchange.

Selectors S200 and S300 may be of a simple, single-motion, step-by-steptype, employing a stepping magnet (245, 346) to advance a set of brushes(248,348), and employing a release magnet (241, 341) to return the brushset to normal position.

DETAILED DESCRIPTION The invention having been described generally, adetailed describtion of the operation of the illustrated apparatus willnow be given.

A. M am exchange to rural exchange The operations involved on a callthrough the main exchange to a rural exchange will first be described.For this purpose, it may be assumed that the subscriber at substationI00, Fig. 1, desires to converse with the subscriber at station 0331 ofthe rural terminating exchange RT, Fig. 3.

Removal of the receiver (not shown) at substation I00 results in theusual operation of line relay I02 to light line lamp I04. The operatormay answer the call by inserting the plug PI of idle cord circuit CCinto jack J I. When this occurs, cut-off relay I03 and sleeve relay I06operate in series. Line relay I02 responsively restores to extinguishline lamp I04. Sleeve relay I06 closes a point in the circuit ofanswering supervisory lamp I08, but this lamp remains extinguishedbecause supervisory relay I07 operates over the calling line through theleft-hand Windings of repeating coil I05.

It will be observed that cord circuit CC is only fragmentarily shown,the usual keys being omitted, including the ringing and listening keys.

The operator may now converse with the calling subscriber in the usualmanner. Upon ascertaining the destination of the call, the operator mayinsert plug P2 into the jack of an idle trunk line extending in commonto the rural exchanges, the jack J2 of the illustrated trunk line TL forexample. When this occurs, sleeve relays III and H2 operate in series.Relay III lights calling supervisory lamp I09 in the cord circuit CO.

The expressions Outgoing and Incoming as used herein are applied to theitems of apparatus to indicate direction of operation or control fromthe standpoint of main exchange. For example, repeater R225 is termed anoutgoing repeater because it handles calls outgoing (in a control thenormal marking ground potential.

to the next succeeding rural exchange.

sense) from the main exchange to a rural exchange and repeater R250 istermed an incoming repeater because it functions on calls incoming (in acontrol sense) from a rural exchange to the main exchange.

In the terminating telegraph repeater R100, sleeve relay I I2disconnects line lamp I I5 and operates outgoing line relay II 4 throughthe normally closed contacts of key K.

Upon operating, outgoing line relay II4 disconnects the main exchangeend of the first section of the associated difierential-duplex telegraphline from ground and connects it to the ungrounded pole of the exchangebattery by way of the adapting resistor II5. By this operation, negativespacing potential is substituted for Thereupon, spacing current flowsthrough both windings of incoming line relay II3 in parallel. Beingdifferentially connected, relay I I3 is not operated by this locallyapplied flow of spacing current.

The flow of current through the lower winding of line relay II3 is toground by way of balancing artificial line II1, illustrated as aresistor and a condenser in parallel. The flow of current through theupper winding of relay I I3 is by way of derived telegraph leg I23,retard coil II9 of the local filter arrangement including antithumpcondenser I20, the upper one of conductors I23, retard coil 2I9, derivedtelegraph leg 222, lower winding of outgoing relay 23I of repeater R200,and thence to ground through contacts of line relays 234 and 235. Linerelay 23I operates as a result of current flow through its lower windingalone, operating outgoing repeating relay 232.

At its lower contacts, outgoing repeating re lay 232 operates line relay24I of outgoing repeater R225. Release relay 242 is operated by linerelay 24I. Among other things, it grounds sleeve conductor S of incomingbranch 249 of the common trunk line in use, thereby guarding the commontrunk line against seizure at intermediate exchange RI.

In the repeater R200, outgoing repeating relay R232 also operates slowrestoring outgoing hold relay 233 for a purpose which will appearhereinafter. At its upper armature, relay 232 switches over the secondsection of the associated telegraph line from its normal markingcondition to spacing condition, thereby supplying current to the twowindings of differential incoming line relay 235 in parallel, whereforerelay 235 is not operated. The circuit path for the upper winding ofrelay 235 includes the balancing artificial line 236 (similar toartificial lines I I1, 2|! and 3 I1). The circuit for the lower windingof relay 235 is by way of the local telegraph leg 237, retard coil 2I 9,and thence by way of the upper conductor 223 to ground through apparatusin intermediate exchange R2, Fig. 4 (not shown in the circuit drawings),including parts similar to 2I9 and 23I.

Operations occur in intermediate exchange R2 as described above forintermediate exchange RI. These operations include the guarding of thecommon trunk line in intermediate exchange R2 and the relaying of thespacing telegraph signal Such signal is further repeated until itreaches rural terminating exchange R3 of Fig. 3, wherein the telegraphcircuit is completed to ground over the upper retard coil 3I9,"localtelegraph leg 320, the

lower winding of-- outgoing line relay R300, and contacts of relay-334.

Relay 331 of the terminating telegraphrepeater' R300 now operates tobring about the successive operation of line and release relays 34:!andBt-Z of outgoing repeater R325; and the latter relay grounds slceveconductor S oi incoming branch 35-9 of the-common trunk line, therebyguarding such trunkline-against: seizure-at the terminating exchange.

As a resultof the above describedoperations; occurring responsive tothe; insertion-0t the plug P2 :into the, jack J 2; theassociatedicommontrunk line has been guarded at: each of therural exschanges tor-Which it extends, and the: exchange selectors (suchassfiilil of Fig. 2531116..5359'015 Fig. 3) have been preparedfor-operation.

In. order to complete the connection; to the desired telephonestation-83311, Fig.- 3; the operatoractuates key. K toassociateihercalling device CD individually. with the: concerned commontrunk line, and then. manipulates. the calling device in accordance withthe digits; in the, desired. telephone number. Operation of key; Ktransfersthe-circuit of the operated outgoing line relay H t tov groundthrough: calling device CD;

The first digit to be dialed. by the operator is a. digit indicativeof:the desired exchange. In the present example, the desired exchange. is.the terminating exchange R'IY' of? Figs- 3.,and 4, to which theexchange. digit dis-assigned- Accord,- ingiy. the operator'firstmanipulatesthe calling device CDito. produceten momentary cireuitimterruptions. representing the exchange digit 0:

Accordingly, outgoing line relay. dis-restored which action is repeatedbyv outgoin repeatin re ay' 32.. low-restoring outs neihold; relay 2353does not respond, to the action of? outgoing repeating r lay. 32. becase: of: hemomentary nature of the. interruption. impulses occasicninghe. i s of. restoration f relay: 3. At. its pper armatu e r lay 8.2 'repatsthe: ten. mo.- mentary markingimpulses; tq -the ext; section f the;telegraph line, with the result that they fina y each. out ing line r ay331 in: e rural terminating exchange, which dine relay; is restoredmomen a yt n. tim s.

In exchange Rt of Fig. 2, line, relay; 2 2i is restored momentarily tentimes by outgoing repeating relay-232; the .slow- -restoringrreleaserelay 2,42 remaining operated; Uponeach restoration ofline relay 2M,animpulse is delivered to ster).- ping-magnet 246- through the backcontact; of the: inner armaturaof line relay 2 51-, and, the frontcontact of l the lower; armature, of. theoperated: release relay 2 3 2;Stepping imagnet 2%. is accordingly energized, ten times to advancebrushes hasten steps fromtheir illustrated nor-. mal: position. Thebrushes are therefore ad.- vanced. to. the-tenth set of bank contacts.(0) corresponding to the ruralterminating. exchange. Thesecontactsareleft: disconnected in allrural exchanges. except, in the ruralterminating ex-. change a RT.

Impulse-series. relay 2&3; connected-in parallel with. stepping. magnet246:; operates responsive tothefirst: impulse of the seriesand remainsoperated throughout the series of impulses, beingslow restoring asindicated.

Both pairs. of off-normal. contacts ON' associated With selector S290:close on. the first step of the brushes 248' from their normal positionand remain; closed. thereafter until. the selector isreturned toitsnormal position.

When seriesrelay 2&3 restores at the end of the series of impulses,switching relay 2&5 operates through the upper contacts of relays: 2%2and. 2 33, and through the upper pair of offnormalacontactstoN. Uponoperating, relay 2'55 locksritself, at its inner upper contacts, toground through contacts. of releaserelay 2 32; disconznects steppingmagnet 2 36, atits inner lower contacts, to prevent impulses transmittedincidentto thedialing of further digits fromeiiectringthe selector; andvperforms other switching operations which-are; of no consequence exceptinv the selected exchange.

Similar operations occurin each other one. of the rural exchanges,. theexchange selector in each being set to thetenth positioncorresponding tothe called terminating exchange RT.

In the terminatingexchange, stepping. magnet 366 off theselectorS3idresponds totheaction of the line relay 3 5i. asdescribedfor.partsZlii and 2, 36, advancing brushes. 3.431 to. the tenthset of contacts (0? which are connectedin theterminating exchange.Switching. relay 365 operates as described for relay 245. 1

In addition to locking itself directly to the upper contacts of relay352: and disconnecting stepping magnet 3465; relay: 3455 places a.bridge across brushes 343; which'includes the winding of polarizedsupervisory relay 3M and thelower contacts of line relayt ll. As aresult, a bridged; calling. condition is placed on the conductor pair3N, extending from. the connected tenth contact set .(0) to thebank offinders such as Fwd, A line'circuit: (not. shown) of'the typeordinarilyemployed for subscriber lines and comprising a line relay and a cut-on:relay, corresponding generally torelays Hi2 and. 803 of line circuit LC,Fig. 1, maybe associated with conductors 3i)! and. the associated.terminals in the finder. bank. Accordingly, the described bridging ofconductors 3% results in thecperation of anidle finder, F380 forexample, to make connectionstherewith.

Finder F38!) is illustrated. as linked with conneotor C303; havingthe-usual control relays, of whichrelays it'll to 313 are shown. Whenfinder Fttt is set onto conductors 30! responsive to the describedbridging thereof, line relay 372 operates over the bridged conductors36! in series with the windingof polarized. supervisory relay 344i Relay3M does not operate at this time. Line relayBlZ brings about theoperation of the associated release relay 373 to ground the associatedsleeve conductor: S and to prepare the connector C398 for operationiii-response to the remaining digits in the desired number.

When the operator manipulates. the calling device CD in accordance withthe remaining digits (3, 3, and 1) in the desired number, correspondingseries of impulses are transmitted over the tandem-related'sections ofthe telegraph line. ihese additional impulses are responded to bylinerelayfifil in intermediate exchange RE, by the corresponding line-relaysinthe remaining intermediate exchanges, and by line relay 34! interminating exchange RT, but no particular result is produced in anyexchange except in-the selected terminatingexchangeRT. For example,

salami in intermediate exchange RI, line ielay 24I causes series relay243 to operate, but produces no other result as the brushes 248 havebeen set on contacts which are locally unwired.

In the terminating exchange RT, line relay 34I restores momentarily as aresult of each impulse of each of the succeeding digits. At its lowercontact pair, it momentarily interrupts the bridge across conductors 30Ieach time it restores, causing line relay 312 of the connector C300 torespond. Series relay 343 operates at the beginning of each additionalseries of impulses dialed and remains operated to the end thereof, butstepping magnet 346 gives no further response as it is disconnected atthe inner lower contacts of the operating switching relay 345.

Upon operating on the first impulse of any further digit, series relay343 disconnects the tip and ring conductors extending forward fromrepeating coil 3I8, to eliminate all but the first inductive disturbancefrom the talking path. Additionally, relay 343 bridges resistor 240around the winding of polarized relay 344 to reduce the inductance ofthe holding bridge during the impulsing operation. The response of linerelay 3'22 of the connector C300 to the impulse series representing thelineselecting digits 3 and 3 causes such connector to be set upon theterminals of the corresponding line in the usual manner, while theresponse of such line relay to the single impulse constituting thestation digit 1 conditions the ringing apparatus of the connector C300to signal the wanted station on the line as distinct from any otherstations which may be connected thereto, the wellknown party-linearrangement.

When the subscriber at the called station 0331 removes his receiver inresponse to being called, the usual tripping operation occurs to closethe indicated connection. Thereupon, supervisory relay 3H operates toreverse the direction of current fiow through the winding of polarizedsupervisory relay 344. Relay 344 thereupon operates to close a circuitfor the lower winding of local line relay 334 of terminating repeaterR300 to signal the operator over the incoming channel of the telegraphline that the call has been answered.

Upon operating, relay 344 disconnects the terminating section of theassociated telegraph line from ground and transfers it to the ungroundedpole of the exchange battery. This constitutes replacing the normalmarking condition on the inward channel by a spacing condition. Thisspacing signal is relayed from one intervening rural exchange toanother, resulting in the operation of incoming line relay 235 ofrepeater R260.

Upon operating, relay 235 closes a point in a second circuit for linerelay 24I, but this circuit is presently being held open by the operatedoutgoing hold relay 233. At its upper armature, relay 235 disconnectsthe first section of the telegraph line from ground and transfers it tothe ungrounded pole of the exchange battery, thereby repeating thespacing signal to the main exchange.

Incoming line relay H3 of the repeater RI in the main exchange nowoperates. Its circuit is from battery through the front contact of relayN4, the lower winding of relay H3, and thence to ground throughartificial line In. Outgoing line relay 23! of repeater R200 is nowmaintained operated over a similar local circuit for its upper winding,the telegraph circuit being currentless.

At its upper contacts, relay, I I3 closes a super visory bridge acrossthe tip and ring conductors of the jack J2, including the resistor I I6and the switchboard windings of repeating coil II8. Supervisory relay H9in the cord circuit CC now operates through the right-hand windings ofrepeating coil II5, thereby extinguishing supervisory lamp I09 toindicate to the operator that the call has been answered.

Conversation may now take place between the subscriber at substation I00(Fig. 1) and the subscriber at called substation 033I (Fig. 3) over thepath indicated by the heavy talking conductors. This talking pathincludes repeating coils I05, H8, and 3l8. It further includes blockingcondenser pairs I2I in the main exchange, 22I and 22I in intermediateexchange RI, and 32I in the terminating exchange RT.

When the conversation has been completed, the replacing of the receiversat the concerned substations results in the lighting of supervisorylamps I08 and I09 of cord circuit CC as disconnect signals. The lightingof lamp I08 occurs directly as the result of the restoration ofsupervisory relay I01 with sleeve relay I06 operated. The lighting oflamp I09 as a, disconnect signal results directly from the restorationof supervisory relay H9 with sleeve relay III operated, whichrestoration results indirectly from the replacement of the receiver atcalled substation 033I. More particularly, replacing of the receiver atstation 033I causes supervisory relay 3' to restore, which in turncauses polarized supervisory relay 343 to restore by returning thedirection of current flow therethrough to normal. Relay 344open-circuits and restores local line relay 334 of telegraph repeaterR300. The terminating section of the associated telegraph line isthereby returned to its normal inward marking condition, which isrepeated through the intervening rural exchanges to the intermediateexchange RI, whereat incoming relay 235 restores and regrounds the firstsection of the telegraph line, whereupon incoming line relay II3 of therepeater RI00 restores to open circuit and restore supervisory relay II0.

If, instead of replacing the receiver, the subscriber at the calledstation 033I desires to attract the operators attention, he may do so byopening his hookswitch (not shown) a number of times momentarily. Foreach momentary opening of the hookswitch, lamp I09 is lighted aspreviously described, and. is extinguished as previously described whenthe hookswitch is allowed to reclose the called line. This operation iscustomarily termed flashing.

Assuming that both subscribers have replaced their receivers, to causelamps I08 and I00 to glow steadily as described, the operator at themain exchange may now take down the connection by removing plugs Pi andP2 of the cord circuit CC. The resultant restoration of sleeve relaysI06 and III extinguishes lamps I00 and I 09, while the restoration ofcut-off relay I03 returns the manual line circuit LC to normalcondition.

The restoration of sleeve relay II2, upon the removal of the plug fromjack J 2, open-circuits and restores outgoing line relay I I 4, whichreturns the outgoing channel of the first section of the telegraph lineto its normal grounded marking condition, thereby restoring outgoingline relay 23I of repeater R200. Outgoing repeating relay 232open-circuits and restores line circuit 33I of repeater 225, causing anincidental momentary operation of series relay 243. Release relay 242restores after an interval and un-- ro s the sleeve conductorsoithelocai r nch 249 ofv the commonhtrunkfllin thereby marking thetrunk, line, as; idle intermediate exchange RI. Additionally, relay N2open-circuits and restores switching relay- 245, whichdisconnectsbrushes Bland closesacircuit for release magnet 241, through thelowersetof, ofienormal cone tacts ON, whereupon magnetj ilreturns brushes 248 totheir normal position in .theusual manner,

In the repeater R236, the continued restoration of outgoing repeatingrelay 332 permits outgoing hold relay 33.3110 restore after an interval,completely clearing out the apparatus inexchange R1. The upperarmatureof,outgoing repeating.rela 332 repeats the normal markintelegraphcom dition to the next succeeding rural exchange, with theresult that itv reaches the terminatin exchange RT,,whereat,outgoingline relay 33!. re-. sponsively restores.

In the repeater R325, line relay34l now re,- stores, causinganincidental temporary Operation of series relay 343; After a; slightinterval, release relay 242- restores, torernove the guarding groundpotential. from the sleeve conductor 3.44

and to permitswitching relay 345; torestore- The selector S300..isc1eared.out as described for the selector S2 00,

The described restoration of line relay 34! opens thebridge acrossconductors-30.! and thereby. open-circuits and restores line relay 312.This is followed amoment later by the restoration of release relay 313to clear, outthe connection through finder; F3300,and;connect9r C39!) inthe usual manner,-

B; Ruralexchunge to mainerchamge In; order o xpl in. h w connectio s romrural-exchang subscribers are completed to, or

through, themain exchange, it may be assumed that thesubscriber atsubstationflafll. (Fig. 3;); in

terminatingexchange RT desires'to converse with the terminals of anidleoneof thecommon inter- .exchange trunklines- TL and switches theconductors of the calling linethrough thereton It may be. assumedthattha illustrated trunk line .TL of Figs. 1 to 3 isidle at. this.time,- which condition is, indicatedlby the absence of aguarding groundpotential of. sleeve conductor S of its incoming branch 3.49; andthatsuch; trunk line is seized, byway of. branchfiiifi.

Line relay 351 otthe repeater Rjiliiinowv operates over the calli glinereleaserelay 362 operating responsive thereto, At itsv inner. contacts,relay stzgrounds the associated sleevcconductor,

thereby marking the trunk-line engaged, andclosing a holding. circuit(not shown) for switches case and F350,

At its upper, contacta, release relayv 352. closes a circuit for theupper winding of, local linerelay litter the repeater R3ilil, ,bywayofbackcontacts of. relays 3 63 and .345. Relay: 33% now operates tosubstitute a spacing potential for the marking {potential normally.applied. totheas c iated s ction, of telegraph, line, causing, theincoming line relay. (not shown). inthe.adiacentjrunal;exchange toperate andreP o t e. cin on i on o the, next succeedin rural 7 exchange.

When the applied spacing condition is repeated to exchange RI, incomingline relay 335 therein operates to repeat at its upper armature, thespacing condition to the section of the telegraph line extending tothemain exchange, At its lower armature, relay 235' operatesline relay 2 ofrepeater R225, through contacts of outgoing hold relay 233. Theoperation of line relay 2 is followed by. the operation of release relay24.2 to prepare the associated selector seen, for operation and toguard1ocalbranch 249 of thetrunk line by applying ground potential to thes1eeve conductor thereof. Similar operations occur in theexchangesintervening betweenRi and RT, with he result that. he. e zommon r nk in s guarded in each of the rural automatic exchangeS.

In the main exchange, incoming line relay H3 responds to the spacingsignal by lighting line lamp H5 roueh on oo so ioo o o oy 2- Theoperator in the main exchange may now nswer the call y se tin e plus o nd e corolv ui ntov theiack J2. the e pera n sl ev r lay I12 o tine i h lmp H 5- dd on-. ally, relay llgroperates outgoing line relay H4 throughcontacts of key Kto place a spacing eonditionon the outgoing channel ofthe associated t r ph line, herebyope a in out o n li relay 23i ofrepeater RZGilin exchange RI. Relays 232 and 233. operate successivelyresponsive to the operation of the relay 23L Relay 232 closes a newcircuit for the operated line relay of re 126M R 25 i r lav 3 3: m si nolay 24! from under. the control of incomin line relay 235.

Outgoing repeating relay 232, at its upper armature, substitutesspacingpotential for marking by the operation successively; of relays 3Mand 342 to prepare the selector $3M for operation responsive to anexchangeselecting digit in the event that the instant call is for a lineof one of the rural exchanges.

The operator in the main exchange may now complete the connection to theline of called station m5 in the usual manner, using the other plug ofthe cord circuit. Assuming that the cord circuit employed istheone-shown at CC, and that the answering plug is P2, theconnectioniscompletedby inserting plug-Pl into jack Ji, causing relays I 63 andlillito operate as described.

Supervisory lamp me lights throughcontacts of sleeve relay Hi6 andremains lighted as a calling supervisory signal until the calledsubscriber answers. It may be recalled that apparatus such as theringing keys and their associated connections have been omittedirom cordcircuit CC to simplify the disclosure;

Answering supervisory lamp Hi9 oi the cord circuit C015 1 01 lightedatthis time because its circuit is held open by supervisory relay Ill],

operated through contacts of theoperated incom- I'i lin relay conversaon, lam s lot. a ie eco e. i h e ;When the two subscribers have finishedtheir as res cti dis oiioo t s a s e p nsive o, h restoration of thereceivers at the two, stations. Res oration thorcoe ver tcall ns s bs at964 causes resto at on. i lino elay 361 1 ceeded by the restoration ofslow-restoring relay 362. Impulse-series relay 363 operates responsiveto a temporary circuit closed by the line relay and opened by therelease relay. The circuit of local line relay 334 of telegraph repeaterR300 is opened initially at the back contact of series relay 353, andthen at the upper contacts of release relay 362. Upon restoring, localline relay 334 replaces marking ground potential on the associatedsection of the telegraph line, which condition is repeated to reachrepeater R200, whereat incoming line relay 235 responsively restores.Its restoration, however, does not affect line relay 24I which is heldoperated by outgoing repeating relay 232.

The replacement of marking potential on the incoming end of the firstsection of the telegraph line, by the upper armature of relay 235,results in the restoration of incoming line relay II3 to restoresupervisory relay I I0, and thereby light supervisory lamp I09 as adisconnect signal.

, If the calling subescriber at substation 034I wishes merely to recallthe operator at the main exchange, as distinct from having theconnection taken down, he may cause the lamp I09 to flash one or moretimes by correspondingly depressing his usual hookswitch one or moretimes rather than by replacing his receiver. Under this condition, thedescribed operations of relays 36I to 363 is followed in each case by areoperation of relays 36! and 362, and the latter relay reoperates localline relay 334 to restore the inward telegraph channel to spacingcondition, causing supervisory relay I I0 to reoperate and extinguishthe momentarily lighted lamp I09.

During this flashing recall operation, the connection through switchesF350 and C350 is maintained by the ground potential applied to sleeveconductor S of branch 349 by release relay 342,

controlled over the telegraph channel from the main exchange, by linerelay 34I. Additionally,

.the guarding potential is maintained on the com- Assuming now that thereceivers have been replaced at both substations to bring aboutdescribed steady lighting of lamps I08 and I09, the operator may takedown the connection. The consequent restoration of sleeve relay I I2permits out going line relay I I4 to restore and replace normal outwardmarking potential on the associated telegraph line, caus ng thedescribed repeating operations to occur which result finally in therestoration of outgoing line relay 33I.

In the first intermediate exchange RI, the restoration of relay 23!causes relays 232 and 233 to restore successively. Relays MI and 242restore successively responsive to the restoration of relay 232, andrelay 242 removes the guarding potential from the sleeve conductor ofincoming. branch 249 of the common trunk line.

In the terminating exchange RT, relays 34! and 342 restore successivelyresponsive to the restoration of relay 33I, and relay 342 removes theholding and guarding potential from conductors S of clear out in theusual manner.

Incidental to the described clearing-out operation, switches S200 and$300 each take a single step when the associated line relay restores,but return to normal position when the associated slow-restoring releaserelay (242, 342) restores.

C. Final rural exchange to first rural exchange In order to explain howconnections from one rural exchange to another are completed, it will beassumed that the subscriber at station 034I in the terminating exchangeRT desires to converse with the subscriber at station I33I of the firstrural exchange RI.

For this purpose, the subscriber at the calling substation 034I removeshis receiver and dials the designation of the main exchange and informsthe main exchange operator of the identity of the called line.

It may be assumed that finder F350 responds as previously described toconnect the calling line to connector C350 upon the removal of thereceiver. Dialing of the designation of the main exchange causes theconnector C350 to operate as previously described to seize an idlecommon trunk line. Assuming the trunk line seized to be the oneillustrated in the drawings, it is seized over branch 349, causingoperations as previously described to occur which culminate in thelighting of line lamp H5. At this time. relays 36I and 362 are energizedin repeater R350; relay 334 is energized in repeater R300; relay 235 isenergized in repeater R200; relays MI and 242 are energized in repeaterR225; and relay I I3 is energized in repeater RI00.

When the operator inserts the plug of the cord circuit in the jack J2 toanswer the call. the resulting operation ofsleeve relay II2 extinguishesline lamp H5 and initiates the previously described succession of relayoperations. This in cludes the operation of relay H4 in repeater I00,the operation of relays 23I to 233 in repeater R200, the operation ofrelay 33I in repeater R300, and the operations of relays MI and 342 inrepeater R325.

Upon ascertaining the number of the called substation, the operatormanipulates key K to associate calling device CD with repeater RI00, andthen dials the number of the called station, comprising exchange digit1, tens digit 3, units digit 3. and station digit 1.

Responsive to the dialing of the exchange digit 1, outgoing line relayH4 is restored once mo- 'mentarily, bringing about a momentaryrestoration of relays 23I and 232 in repeater R200, relay 33I inrepeater R300, and of line relays 24I and 34I of repeaters R225 andR325. Selectors S200 and S300 (together with the selectors at the otherrural exchanges not illustrated) respond as previously described toadvance brushes 248 and 348 to the position corresponding to the calledexchange. In the present example, wherein the first exchange RI iscalled, the selectors are advanced a single step responsive to thesingle impulse constituting the exchange digit. All selectors exceptS200 arrive on disconnected contacts, but selector S200 arrives on itsconnected first set (1) from which conductors 20I extend to contacts inth bank of finder F200. Series I relays 243 and 343 operate inconjunction with the ofi-normal contacts of their respective selectorsdigit.

In the called intermediate exchange RI, the

- :operation of switching relay 245 results in the bridging ofconductors 20I to cause a finder such essential 13 "as F260 to makeconnectiontherewlth whereupon relays 212 and 213 of the associatedconnector C290 operate to prepare the connector-"for operation inresponse to the remaining digits on the number.

In the calling rural exchange RT, the operation of switching relay 345results 'in the opening, at the back contact of its upper armature-cfthe energizing circuit of local line relay 33 3. When this occurs, line'relaysta' l, 235, and H3'restore successively. At its upper contacts,relay 1 l3 open-circuits supervisory relay 1 H1 in "cord cir- "cuit'CC(assumingthat plug P2 was usedto answer the call), lighting lamp 1%through-contacts of sleeve relay HI answered supervisory signal. Thefurther progress of the connection is accordinglyunder the "samesupervisory-signal conditions as obtained when the operator iscontemplatingrt-connection as previously described to one of the rural"exchanges originated at the main exchange, or at "some point beyond.

Responsive to the dialingof the tens "and units digits 3 and 3, theconnector'C'Zdii is set'upon'th'e terminals of the line of the calledsubstation lts'l,

the "controlling impulses being repeated by'the lower contacts of linerelay 2M, intothe "bridge across conductors 2M, through contacts of theoperated relay 2% and brushes 2&8. Seriesrelay "243 responds during eachimpulse series, as ex- "plained herein'before for relay t lt, "andshunts resistor 24% around the winding "of supervisory relay 2 44 toimprove the impulsing circuit for the connector.

Responsiveto the dialing of the st'ation'digit 1, the 'calle'd stationon the called line is selected and is signaled in the usual manner.

When the callis answered,theresulting operation of supervisory relay 2?!causes "polarized supervisory relay 2 14 to operate and close anoperating circuit for local line relay res. Upon "operating, line relayt l switches over the local end of the first section of the telegraphline from its normal marking condition to "spacing condi-"tiongreoperating relay E E3. supervisorytrel'ay illl "responsivelyreoperates to "extinguish lamp "iflliito signal the operator that thecall has been answered.

Since its inner upper armature is discormected,

at the back contact of outgoing "hold relay 5253,

local line relay 2% exercises no control 'at this time over the outgoingchannel oi'thetelegraph line.

Ihe middle armature and the outer armature 'of relay 234, together withtheir back and front contacts, comprise a reversing switch with respectto the connections between the contacts of the upper armature of linerelay 235 and the conductors over which negative spacing potential andmarking ground potential are supplied thereto. Accordingly, relays 23dand .3235 exercise dual control over the inward channel onthe firstsection of the telegraph line. Spacing groun'dpotentia'l is appliedthereto vihenboth relays are .re-

stored, as well as when'both are operated. Negative spacing potential isapplied when either relay Lls operated at the "time when the other isrestored.

Bycontrol exercised through'repeater R35fl;the calling subscriberma yrecall the operator at any time, whether the receiver at the calledstati'onis removed, or is in place. The repeaterRfilLhowever, 'is soarranged that th calling subscriber may not transmit "dial "pulses tothe telegraph line to position the 'switching'apparatus in the calledexchange. "This results from the fact fil'at "the to give the operator"an unrcontrol'is exercised'ithroug'hslow-restoring relays 3152 and363,;which will not follow dial pulses.

openlng the hookswi-tch :at the calling station can causes line -r'e'lay"36 I "torestO-re and operate rlay363ifollowed a moment later by therestoration successivelyof slow-restoringrelays 3'62 and 363.iR'eclosure of the hookswitchcontacts causes relays "3 5! and 3&2to'reoperate successively.

'I'f'th'e described resignalling -operation of relays 361 to 363 occursbefore the operator has dialed the numben'localline re1ay 334 isbeingiheld opera-ted throughthe back contacts of relays 3- 55 and 352."Consequently, rl'ay 't'iid restores responfsive'to the temporaryoperation of slow-restoring relayfllaii, and remains restored untilrelay 3'63 "has restored and relay 362 has reoperated. Theconsequent'tlegraphic signal causes relay Hs'to '"restore temporarily tocontrol supervisory relay H 6 to' fia'shlamp l 8 9.

If the described resign'all'ing operation of relays 36! to 353 occursafter the operator' ha's dialed the exchange "digit, and thereby causedswitching relay 3'45 to "operateiasdescribed to restore relay 33 l"tolightlampllw, then the'operation of relay '3't3closes acircu'it "forrelay '33"; through'a front contact "of "relay 345. Relay 334"accordingly 0p- "erates responsive to "the operation of relay 363, andremains operated until "relay 362 restores, thereby"telegraphicallycontrolling relay '5 H3. If this occurs before the called subscriberanswers, or after he'h'as replaced his receiver, thethen restored .relayH6 is momentarily reoperated to "momentarily extinguish lamp Hi9. 'Onthe other hand, after the called subscriber has "answered, andibeforehehas: replaced -his receiver, local line relay23 l ofthe repeater'R'ZGWisbeing'held operated by supervisory'relay 24 1 of repeater'RQZ'E;relay H0 is operated; and lamp m9 is extiniguished. Under thiscondition, the temporary r operation of incoming line relay 235,responsive to the-described temporary reoperation of local "line relayEEK-causes relays '5 l3 and till to restore temporarily, temporarilyreligliting super- 'vi'sory lamp -lfl'9.

*It will-be understood-of course, that a momentary response is obtainedas above described at supervisory lamp lli'fi when th receiver is re-'placedat the calling substation at any time after theopera-torhasdial'ed the'exchange digit. The operator'ma-y disregards.single flash-of a supervisory lamp such as 469, giving heed only to two*or moresu'cc'essive flashes, such as are caused by two or moretemporary openings of the hookswitch.

Release 'relay 342, held operated by line relay 3 H "as long'as theoperators cord is connected with the common trunk line, holdsgroundpotential "on "the sleeve conductor of branch 349 to*rnaintainswitchescfi-fi dand'Fdfi in operated condition "during'thetimere'lay 362 is restored.

When the receiver isreplaced atthe called sub- "station, the consequentrestoration of supervisory "relay 36'! -causes sup-ervisoryrelay 2M torestore, responsiveto which local-line relay 2% in the repeater R258restores'and returns the first section of the associated "telegraph"line to its normal marking condition. When this occurs, line relay'IIS'and supervisory relay Hi3 restore, relighting 'supervisorylamp :cs.Recl'osing of the line at the "called station at any time before theconnection is taken-down reverses the describedrelay operation, to againextinguish lamp use, as when the "called subscriber actuates' hishookswitch to 'recali the operator.

15 their receivers, and that lamp I09 is lighted steadily as adisconnect signal, the operator may remove her plug from the jack J2 tobreak down the connection. When this occurs, the restoration of outgoingline relay II4 reimpresses the normal marking condition on theassociated telegraph line, which is repeated through repeater R200 andthe other similar repeaters to reach repeater R300, line relays 23I and33! restoring.

In the repeater R200 the restoration of line relay 23I is followed bythe restoration successively f relays 232 and 233 to return the repeaterto its illustrated normal condition.

In the repeater R225, relays 24I and 242 restore successively responsiveto the restoration of relay 232. Relay 245 restores responsive to therestoration of release relay 242. Branch 249 of the illustrated commontrunk line is rendered available to the local switches by the removal ofground potential from the sleeve conductor thereof by relay 242.

Switches F200 and C200 are cleared out in the usual manner responsive tothe opening of the local contacts of line relay 24 I, followed a momentlater by the described restoration of relays 242 and 245. Steppingswitch S300 is cleared out in the previously described manner responsiveto the estoration of relay 242.

In the calling exchange RT, the restoration of outgoing line relay 33Ipermits relays 34L 342, and 345 to restore successively. Relay 342removes the guarding and holding ground potential from the sleeveconductor of branch 349. This operation renders the common trunk lineagain available to the local switches and permits switches C350 and F350to clear out. Selector S300 clears out as previously describedresponsive to the restoration of relay 342.

D. First rural exchange to final rural exchan e In order to furtherexplain the provisions for handling calls from one rural exchange toanother, the operations involved in a call from a line of the firstrural exchange RI to a line of the final rural exchange RT will beoutlined. For this purpose, it may be assumed that the subscriber atstation I33! of the first rural exchange desires to converse With thesubscriber at station 033! of the terminating rural exchange.

It may be assumed that finder F250 operates responsive to the removal ofthe receiver, to extend the line of calling station I34! to connector0250, and that connector C250 finds the illustrated common trunk lineidle when the designation of the main exchange is dialed, seizing suchtrunk. line by way of branch 249, relays 26I and 202 operating.

The operation of relay 202 closes a circuit, by way of contacts of theunoperated relays 263 and 245, for local line relay 234. At its innerarmature, relay 234 switches the second section of the telegraph linefrom its normal marking condition to spacing condition, which isrepeated through the intervening rural exchanges to the terminatingrural exchange, whereat outgoing line relay 335 operates. The repeaterR325 is thereby prepared for operation as previously described (relaysSM and 342 operating), guarding the common trunk line from seizure inthe terminating exchange. The common trunk line is similarly guardedagainst seizure in each intervening exchange.

By the operation of the upper armature of local line relay 234 of therepeater R200, a marking condition is transmitted over the first sectionof the telegraph line to operate incoming line relay I I 3 in the mainexchange to light line lamp I I5 as a calling signal.

The operator may respond to the calling signal by inserting the plug ofan idle cord circuit into the jack J2 with the previously describedresults, including the extinguishing of line lamp H5 and the operationof outgoing line relay II4 to impress a spacing condition on theoutgoing channel of the associated telegraph line.

- -In the repeater R200 located in the calling rural exchange, linerelay 23I responds to the outgoing spacing potential to operate relays232 and 233 successively. At its upper armature, relay 232 takes overthe control of the second section of the telegraph line and makes asubstitute spacing connection thereto (initially made by local linerelay 234) whereby a spacing condition is maintained on the succeedingsections of the telegraph line.

At its lower contacts, relay 232 operates line relay 24I, which operatesrelease relay 242 to prepare repeater R225 and the associated selectorS200 for operation. Relay 242 places an additional ground potential onthe sleeve conductor S of the associated branch 240 to hold the operatedswitches F250 and C350 so long as the connection remains establishedthrough the jack J2 in the main exchange.

The operator may now associate her calling device CD temporarily withthe illustrated common trunk line and dial the called number (033I).Operations as previously described now occur in the repeaters R225 andR325 to position the selectors S200 and S300 on the tenth (0) contactset, followed by the operation of switching relays 245 and 345.

In the called exchange RT the operation of relay 345 causes brushes 348to be bridged through relay 344 and contacts of line relay 34I,whereupon a finder such as F300 operates in the usual manner to extendthe connection to a connector such as C300.

In the calling exchange, the operation of switching relay 245 serves toopen-circuit and restore local line relay 234. With relays 232 and 233operated, the marking condition imposed on the associated end of thesecond section of the telegraph line is not disturbed. Restoration ofthe upper armature of relay 234 returns the normal marking potential tothe first section of the telegraph line, restoring incoming line relayII3. Assuming that it is plug P2 of the cord circuit CC which is in use,supervisory relay IIO responsively restores to light supervisory lampI09 to give unanswered supervision to the operator.

Responsive to the dialing of the remaining digits of the number, theconnector C300 is set upon the called line and applies ringing currentto signal the called station.

When the call is answered, relays 3', 344, 334, 235, H3, and I I0operate, relay IIO extinguishing lamp I09 to give answered supervision.

With the connection from the calling station I34I through switches F250and C250 held under operator control by release relay 242, and with theconnection through switches F300 and C300 held under operator control byline relay 34I, either subscriber may signal the operator as describedin connection with the call from exchange RT to exchange RI.

When both subscribers to the connection have replaced their receivers,lamp I09 is lighted steadily as a disconnect signal, whereupon theoperator may remove her plug from the jack J2 to E. Operator control ofintra-erchange connections Each rural exchange is provided with circuitarrangements enabling the operator to complete locally a connectionoriginating therein when requested to do so. In order to describe thesearrangements, it may be assumed that the'subscriber at substation 03M ofthe terminating exchange desires to converse with the subscriber atsubstation 033I of the same exchange, and desires the operator at themain exchange. to set up the connection. This situation may arise whenthe main-exchange operator has been called for information as to thenumber of the called station.

It may be assumed that the; calling line has been extended .to the mainexchange through finder F350, connector C350, and the illustrated commontrunk line, and that the operator has answered the call by inserting theplug P2 into the jack J2 with results as described.

Responsive to the dialing of the exchange digit, 0 in the number of thecalled station, the selectors such as S200 and S300 operate aspreviouslydescribed, and selector S300 makes connection with conductors I to causean idle finder such as F300 to bring in a local connector such as C300.

Switching relay. 345, on operating following the dialing of the exchangedigit, restores localline relay ass as previously described.Consequently relays 235, H3, and H0 are. restored, wherefore lamp I00 islighted to give unanswered supervision to the main-exchange operator.

Connector C300 operates in the usualmannerto connect with the calledline and to. signal the called station 033I thereon responsive to thedialing of the remaining digits in the called number.

When the called subscriber answers, the resulting operation ofsupervisory relay 3' causes polarized supervisory relay 344 to operate,operating local line relay 334 to transmitanswered supervisiontelegraphically to the main exchange. Relays 235, I I3, and I I0responsively operate, and relay lid extinguishes supervisory lamp I09 togive answered'supervision.

Either subscriber to the locally completed .connection may now recallthe operator by momentarily depressing his hookswitch. If the subscriberat the called station 033I signals the operator, polarized supervisoryrelay 344 responds to the resulting'momentary restoration of relay 3' tosignal the operator through the resulting action of local line relay334. On the other'hand, if the subscriber at the calling substationmomentarily depresses his hookswitch, relays 30I to 303 respond aspreviously described anda circuit is momentarily closed for local linerelay 334 through front contacts of relays 362,303,- and 345. Local linerelay 234 is diiferentially wound, and the lower winding is beingmaintained energized through contacts of polarized relay 344.Consequently, the momentary energizationof the upper winding responsiveto actuation of the hookswitch contacts causes relay 334 to restoremomentarily and to transmit a momentary marking signal telegraphicallyto the main exchange, whereat relay II3 restores momentarily to causesupervisory relay IEO to momentarily'extinguish supervisory lamp I09.

When both subscribers to the connection have 1% replaced. theirreceivers, lamp I00 glows steadily as a disconnect signal. The entireconnection clears out (including finders F350 and F300 and ofconnectorsC350 and C300) responsive to the removal of the plug from jackJ2.

F. Modified guarding arrangement Fig. 4 shows a modified arrangement forguarding the common trunk line TL of Figs. 1 to 3 against seizure at theremaining rural exchanges responsive to seizure at any one of them. Inthe arrangement of Figs. 1 to 3, it will be recalled that transmitting aspacing signal over the outward channel from the main exchange causesrelease relays 2-52 and 302 to operate to guard branches 2&0 and 349 ineach of the rural exchanges. It will be recalled further that seizure ofthe common trunk line in any rural exchange signals the main-exchangeoperator over the inward telegraph channel, and operates to guard theseized trunk line against seizure in each of the other rural exchanges.This guarding provision for use in the repeater R200 when the commontrunk line is seized at a more remote rural exchange includes the lowercontacts of incoming line relay 235 for operating relay 2M to therebyoperate release relay 242. On a seizure of the common trunk line atrural intermediate exchange RI, local line relay 234 operates to signalthe main exchange operator at its upper armature and front contact, andoperates at its inner armature and front contact to transmit a signalover the outgoing telegraph channel to cause the common trunk line to beguarded at the rural exchanges more distant from the main exchange.

. In the arrangement shown in Fig. 4, the repeater RI00 at the mainexchange is arranged to respond to the operators calling signal over theincoming telegraph channel to transmit a signal back to all the ruralexchanges over the outgoing telegraph channel to thereby guard theseized common trunk line in each.

The repeater P.I00 of Fig. 4 is exactly similar to the repeater RI00,except that incoming line relay I I3 has an added armature I30 foroperating outgoing line relay H4.

The intermediate telegraph repeater R200 of Fig. 4 corresponds generallyto repeater R200 of Fig. 2, but outgoing repeating relay 232 andoutgoing hold relay 233 of the latter repeater are omitted.Additionally, outgoing line relay 23I is arranged to control the outwardtelegraph channel and the local signal branch directly, while local linerelay 234 and incoming line relay 235' have no function except toexercise joint control over the next succeeding inward section ofthetelegraph line, as described hereinbefore for the middle and upperarmatures of relay 234, and the'upper armature of relay 235.

I In order to describe further the modified arrangement of, Fig. 4, itmay be assumed that the repeater RI00 is substituted in the arrangementof Figs. 1 to 3 for the repeater RI00, and that the repeater R200 ofFig. 4. is substituted for repeater'R200 at each rural intermediateexchange. Repeater R300 at the rural terminating exchange remainsunaltered.

Seizure of the associated common trunk line at the main exchange,through jack J2, causes sleeve relay H2 to'operate outgoing line relayll4as hereinbefore described. The consequent transmission of a negativespacing telegraph signal over telegraph legs I22 and 222 in seriescauses outgoing line relay 23I to operate. Atits lower contacts, relay23I operates line relay 2M, which in turn operates release relay 242 toguard branch 249 against seizure.

Outgoing line relay 23!, at its upper armature, repeats the spacingpotential to the next succeeding section of the telegraph line, with theresult that similar operations occur in the next succeeding exchange toguard the common trunk line thereat and to repeat the spacing signal tothe next rural exchange.

When the repeated spacing signal reaches the terminating exchange of Fig3, relays 33!, 3M, and 342 operate as previously described, and relay342 guards the trunk line against seizure.

With the modified repeaters R100 and R200 of Fig. 4 substituted ashereinbefore assumed, seizure of the common trunk line at rural exchangeRI results in the operation of local line relay 234, Fig. 4, ashereinbefore described for local line relay 234, resulting in thetransmission of a spacing signal inwardly over conductors 222 and I22 tooperate incoming line relay H3. In addition to lighting line lamp H5 asa call signal, relay H3, at its armature I80 and front contact, operatesoutgoing line relay H4 thereby causing the associated common trunk lineto be guarded against seizure in each of the rural exchanges as abovedescribed.

When the common trunk line is seized in the rural terminating exchangeRT of Fig. 3, local line relay 334 operates as previously described totransmit a spacing signal over the inward telegraph channel. Thisspacing signal is repeated at the intervening exchanges to reach thesubstituted repeater R200 in the rural intermediate exchange RI.Incoming line relay 235' there upon operates to repeat the spacingsignal to the main exchange. Relay H3 accordingly operates as describedto light line lamp I I5 and to operate outgoing relay H4 to cause theseized trunk line to be guarded in each of the rural exchanges, as wellas to prepare the apparatus in each rural exchange for the receipt ofimpulse series for controlling the switching apparatus.

I claim:

1. In a multi-exchange telephone system, a two-way trunk line extendingin common between a first exchange and a plurality of other exchanges,means in any said exchange for tak-. ing the common trunk line for use,and means responsive thereto for marking the trunk line busy in eachother said exchange, the last-named means including two mutuallyindependent telegraph channels and means for signalling over one or overboth depending upon the exchange at which the common trunk line is takenfor use.

2. In a multi-exchange telephone system, a two-way trunk line extendingin common between a main exchange and a plurality of subordinateexchanges, the trunk line including a talking channel and two telegraphchannels respectively outgoing from and incoming to the main exchange,means in each said exchange for taking the common trunk line for use, acalling signal in the main exchange, means in each subordinate exchangefor marking the trunk line busy thereat, means responsive to the trunkline being taken for use in the main exchange for controlling the saidbusy-marking means in each subordinate exchange over the outgoingtelegraph channel, and means responsive to the trunk line being takenfor use in any subordinate exchange for controlling said calling signalover the incoming telegraph channel.

8. In a multi-exchange telephone system, a two-way trunk line extendingin common between a main exchange and a plurality of subordinateexchanges, the trunk line including a talking channel and two telegraphchannels, respectively outgoing from and incoming to the main exchange,meansin any said exchange for taking the common trunk line for use, acalling signal in the main exchange, means in each subordinate exchangefor marking the trunk line busy thereat, means responsive to the trunkline being taken for use in the main exchange for controlling the saidbusy-marking means in each subordinate exchange over the outgoingtelegraph channel, means responsive to the trunk line being taken foruse in any subordinate exchange for controlling said calling signal overthe incoming telegraph channel, and means in at least one subordinateexchange for controlling said busymarking means thereat over theincoming telegraph channel responsive to seizure of the common trunkline at another subordinate exchange.

4. In a multi-exchange telephone system, a two-way trunk line extendingin common between a main exchange and a plurality of subordinateexchanges, the trunk line including a talking channel and two telegraphchannels respectively outgoing from and incoming to the main exchange,means in any said exchange for taking the common trunk line for use, acalling signal in the main exchange, means in each subordinate exchangefor marking the trunk line busy thereat, means responsive to the trunkline being taken for use in the main exchange for controlling the saidbusy marking means in each subordinate exchange over the outgoingtelegraph channel, means responsive to the trunk line being taken foruse in any subordinate exchange for controlling said calling signal overthe incoming telegraph channel, and means in at least one subordinateexchange responsive to the trunk line being taken for use therein forcontrolling the busy-marking means in at least one other subordinateexchange over the outgoing telegraph channel.

5. In a multi-exchange telephone system, a two-way trunk line extendingfrom a main exchange to a terminating subordinate exchange by way of atleast one intermediate subordinate exchange, the trunk line including atalking channel and two telegraph channels respectively outgoing fromand incoming to the main exchange, means in any said exchange for takingthe trunk line for use, a calling signal in the main exchange, means ineach subordinate exchange for marking the trunk line busy thereat,

means responsive to the trunk being taken for use in the main exchangefor controlling the said busy-marking means in each subordinate exchangeover the outgoing telegraph channel, means responsive to the trunk linebeing taken for use in any subordinate exchange for controlling saidcalling signal over the incoming telegraph channel, and for controllingthe busymarking means in any succeeding subordinate exchanges over theoutgoing telegraph channel, and means in said intermediate exchangeplacing the busy-marking means thereat also under the control of theincoming telegraph channel.

6. In a multi-exchange telephone system, a

. two-way trunk line extending in common between a main exchange and aplurality of subordinate exchanges, the trunk line including a talkingchannel and two telegraph channels respectively outgoing from andincoming to the main exchange, means in any said exchange for 21 Itaking the common trunk line-for use, a calling signal in the mainexchange, means in each subordinate exchange for marking the trunk "linebusy thereat, means responsive to the trunk line being taken for use inthe main exchange for controlling the said busy marking means in eachsubordinate exchange over the outgoing telegraph channel, meansresponsive to the trunk line beingtakenfor usein' any subordinate ex-'change for controlling said calling signal over the incoming telegraphchannel, and means also controlled over the incoming telegraph channelfor controlling the busy-marking means in each subordinate exchange overthe outgoing channel. 7. In a multi-exchange telephone. system, a

trunk line extending between a first exchange and 'a second exchange,an'operators switchboard in the first exchange, means in the secondexchange for connecting a calling line to the operators switchboard byway of said trunk line and for applying a quiescent supervisorycondition thereto, means controlled over the trunk line for theoperators switchboard for extending a connection from said calling lineto a called line, means in the second exchange responsive thereto forsubstituting an active supervisory condition for the quiescent one,means responsive to answering on the called line for restoring thequiescent supervisory condition to the trunk line during conversation,means controlled from the calling line after said connection has beenextended to the called line for substituting the currently unapplied oneof said supervisory conditions for the applied one, and operatorssupervisory means controlled according to whether said quiescent or saidactive supervisory condition is applied to the trunk line.

8. In a multi-exchange telephone system, a trunk line extending betweena first exchange and a second exchange, an operators switchboard in thefirst exchange including means for making connection with the trunkline, means in the second exchange for connecting a calling line to theoperators switchboard by way of said trunk line and for applying aquiescent supervisory condition, means controlled over the trunk linefrom the operators switchboard for extending a connection from saidcalling line to a called line, means in the second exchange responsivethereto for substituting an active supervisory condition for thequiescent one, means responsive to answering on the called line forrestoring said quiescent supervisory condition during conversation,means controlled from the calling line at any time said connectionexists therefrom to the first exchange and to the called line fortemporarily reversing said supervisory conditions, and operatorssupervisory means controlled according to whether a quiescent or anactive supervisory condition is applied to the trunk line.

9. In a multi-exchange telephone system, a trunk line extending betweena first exchange and a plurality of other exchanges, an operatorsswitchboard in the first exchange, means in any said other exchange forconnecting a calling line thereof to the operators switchboard by way ofsaid trunk line and for applying a quiescent supervisory conditionthereto, means controlled over the trunk line from the operatorsswitchboard for extending a connection from any said calling line to acalled line, means in the exchange containing the calling lineresponsive thereto for substituting an active supervisory condition forthe quiescent one, means responsive to answering on the called line forrestoring the quiescent supervisory condition to the. trunk line-,1during conversations and operators supervisory means controlledaccording, to whether said quiescent or said active supervisorycondition is 1 applied to the trunk line.

operators switchboard by way of said trunkline and f for applying twosupervisory conditions, alternatively to said trunk line dependingupon",

whether the hookswitch contacts on the calling line are open or arelclosedameans controlled over the trunk line from the operatorsswitchboard for extending a connection from said calling line to acalledline, means. in the second exchange responsive thereto fortransferring the control over said supervisory conditions to the calledline, and means thereupon rendered effective for temporarily reversingsaid supervisory conditions responsive to an opening of the callingline, and operators supervisory means controlled according to whethersaid quiescent or said active supervisory condition is applied to thetrunk line.

11. In a multi-exchange telephone system, a trunk line extending betweena first exchange and a second exchange, an operators switchboard in thefirst exchange, means in the second exchange for connecting a callingline to the operators switchboard by way of said trunk line, means forapplying a quiescent supervisory condition and an active supervisorycondition alternatively to said trunk line, means controlled by thehookswitch on the calling line for determining which of said supervisoryconditions is current applied, means controlled over the trunk line fromthe operators switchboard for extending a connection from said callingline to a called line, means in the second exchange responsive theretofor placing the determination of said supervisory conditions under thejoint control of the hookswitches on the calling and called lines, andoperators supervisory means controlled according to whether saidquiescent or said active supervisory condition is applied to the trunkline.

12. In a multi-exchange telephone system, a trunk line extending from afirst exchange to distant exchange apparatus, an operators switchboardin the first exchange from which said trunk line extends, means includedin said distant exchange apparatus for connecting a first line and asecond line successively to said trunk line, means controlled by thehookswitch on the first line prior to the connecting of the second lineto the trunk line for placing a quiescent and an active supervisorycondition alternatively on said trunk line, means controlled jointly bythe hookswitches on the two lines for placing said supervisoryconditions alternatively on the trunk line after the second line isconnected thereto, and operators supervisory means at said switchboardcontrolled according to whether said quiescent or said activesupervisory condition is applied to the trunk line.

13. In a multi-exchange telephone system, a trunk line extending from acontrol exchange to a series of succeeding controlled exchanges, meansin each said exchange for connecting a line thereof to said trunk lineto place a pair of such lines in mutual telephonic communication, localsupervisory relays in said controlled exchanges respectively, means forcontrolling each said relay through the hookswitch of a line of thecorresponding exchange which may be currently connected to said trunkline, means rendering each said relay efiectlve to transmit twosupervisory conditions alternatively to the next preceding exchange, arepeating supervisory relay in each controlled exchange except the lastfor repeating said supervisory conditions to the next precedingexchange, the foregoing means including means enablin any said repeatingsupervisory relay and the associated local supervisory relay todetermine jointly which of the two alternative supervisory conditions isto be transmitted to the next preceding exchange, and supervisory meansin the said control exchange selectively responsive to said supervisoryconditions.

BERT A. WALLACE.

24 REFERENCES CITED The following references are of record in th file ofthis patent:

Automatic Telephony, second edition, by

Smith and Campbell, published by McGraw-Hill Book Co.

